/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshQueryFunctions.h
Compute the interpolated Normal (A*Normal1 + B*Normal2 + C*Normal3), where (A,B,C)=BarycentricCoords and the Normals are taken from the specified TriangleID in the Normal layer of the TargetMesh.
static [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * GetInterpolatedTriangleNormal ( [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * TargetMesh, int32 TriangleID, FVector BarycentricCoords, bool & bTriHasValidNormals, FVector & InterpolatedNormal )